The faster the dive, the louder the sound - which may help attract the female by indicating flying fitness.

Scientists showed that the sounds are produced when flowing air hits the bird's tail feathers, causing them to flutter like flags in a breeze.

Adjacent feathers fluttering at different frequencies could create a musical "symphony" of sound.

Some hummingbirds even produced two tones with their tail while singing at the same time.

Dr Christopher Clark, from Yale University in the US, and colleagues wrote in the journal Science: "Our work shows that the tail of male bee hummingbirds functions as an acoustic organ, and we suggest that sexual selection through female choice for flutter-induced sounds has driven the evolution of diversity in male tail morphology."